1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to virtual cell management for interference suppression and interference cancellation in LTE.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A wireless communication network may include a number of eNodeBs that can support communication for a number of user equipments (UEs). A UE may communicate with an eNodeB via the downlink and uplink. The downlink (or forward link) refers to the communication link from the eNodeB to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the eNodeB.
Evolved NodeBs (eNBs) of a network may be pooled together as virtual cells so that they can be treated as one large resource by network managers and users alike. Each virtual cell may include a group of physical cells that may jointly serve a UE. A virtual cell may include a set of macro cells, a macro cell and a relay, etc.
4G LTE Advanced coordinated multipoint (CoMP) systems may be used to send and receive data to and from a UE coordinated by several points to ensure the optimum performance is achieved even at cell edges. LTE CoMP is essentially a range of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations. The aim is to improve overall quality for the user as well as improving the utilization of the network. Essentially, LTE Advanced CoMP turns the inter-cell interference (ICI) into a useful signal, especially at the cell borders where performance may be degraded.
CoMP may have a plurality of transmission modes, e.g., Joint Processing (JP) mode, dynamic point selection (DPS), joint reception, Coordinated Scheduling/Beamforming (CS/CB) mode, etc. In JP mode, the downlink data for a mobile device may be transmitted from several locations simultaneously (Joint Transmission). A simpler alternative is DPS, in which data is available at several locations, but the data is generally sent from one location at any one time. In CS/CB mode, the downlink data for a mobile device is typically available and transmitted from one point. The scheduling and optional beamforming decisions are generally made among all cells in the CoMP set. Locations from which the transmission is performed can be changed semi-statically.
CoMP may generally have four different deployment scenarios: homogeneous network intra-eNB CoMP (Scenario 1); homogeneous inter-eNB CoMP (Scenario 2); heterogeneous network in which eNBs are configured with different physical cell identities (PCIs) (Scenario 3); and heterogeneous network in which eNBs are configured with the same PCI (Scenario 4). Scenario 1 and Scenario 2 are both for homogeneous networks, and differ in whether optical fiber is deployed between physical nodes for backchannel communications. In Scenario 2, the optical fiber permits an eNB to operate remote radio heads (RRH) for CoMP over a larger area. Scenario 3 and Scenario 4 are both for heterogeneous networks but also differ in that, in Scenario 4, low power transmitters in the area of a macro cell are allowed to share a same physical cell identity as the macro cell.
In Scenario 1, a single eNB base station site may be comprised of three or more cells, each being responsible for a sector. In this scenario the eNB may control each of the three or more cell schedulers. In this way, it is possible to schedule a joint transmission by several cells of the eNB or to blank out the resource blocks in one cell that are used in another cell for a subscriber located in the area between two cells to reduce interference. This CoMP approach is easy to implement as no external communication to other entities is required. However, this CoMP approach lacks coordination with other eNBs. As a result, data rates for mobile devices that are located between two cells of two different eNBs may not be improved.
In Scenario 2, two or more RRHs may be distributed over an area and be connected to a single eNB over fiber optic links. These fiber optic links may transport a fully generated RF signal that the RRH converts from an optical signal into an electromagnetic signal that is then transmitted over the antenna. While this CoMP approach can coordinate transmission points in a much larger area than the first approach, its practical implementation may be more difficult as a fiber infrastructure must be put in place to connect the RRHs with the central eNB. A traditional copper wire-based infrastructure may be insufficient for this purpose due to the very high data rates required by the RF signal, the low latency requirement for coordination among the nodes, and the length of the cabling.
In Scenarios 3 and 4 another CoMP approach utilizes several low power transmitters in the area of a macro cell to cover hotspots, such as parts of buildings and different locations in shopping malls. This approach achieves general coverage via a macro cell and offloads localized traffic via local transmitters with a very limited range, thus, reducing the interference elsewhere. The implementation can be performed in two ways. The localized transmissions may have their own cell IDs and, thus, act as independent cells from a mobile device point of view. From a network point of view, however, those cells are similar to RRHs with a lower power output instead of a high power output as in Scenario 2. Another option may use RRHs, as defined above, with a low power output, but without a separate cell ID. In this case, the local signal becomes indistinguishable from the macrocell coverage for the mobile device. Again, fiber optical cabling is required to connect the low powered transmitter to a central eNB.
Interference suppression and interference cancellation may be performed by UEs as measures to improve communications. Many techniques for interference suppression and interference cancellation have been developed and implemented in various ways. In general, interference suppression and interference cancellation need to consider intra-cell and inter-cell interference, homogeneous and heterogeneous networks, control and data channels, and a wide range of signal to interference plus noise ratio (SINR) values. However, the introduction of CoMP introduces a set of features that is generally unfriendly for interference suppression and interference cancellation.